Distinct semiconductor integrated circuits or microchips (or chips) are generally manufactured on a single wafer of semiconductor material (e.g., silicon). These individual microchips are later cut out of the wafer. Each microchip has contact pads that are electrically coupled to the electrical circuitry embedded therein. While the contact pads are exposed in wafer or microchip form, which is before the microchips are packaged, a selected number of microchips are tested by automated test equipment that utilize probe rings and probe cards to test the microchips to ensure they meet design specifications.
Referring to FIG. 1, a probe card assembly 50 generally consists of printed circuit board 10 that has central opening 11 which provides access to the microchip 20 to be tested, together with a series of spaced conductive individual flexible metallic needles or blades (probes) 12 arranged on a metal or ceramic probe ring 13 around central opening 11. Each probe 12 extends away from printed circuit board 10 toward the center of central opening 11. Probes 12 are adapted to electrically contact selected parts on the microchip 20 being tested (e.g., contact pads) which are electrically coupled to the rest of the integrated circuitry embedded in the microchip 20, so that electrical signals may be transmitted to and from the microchip 20 being tested. These signals transmit test routines that test the functionality of circuits and subcircuits of the overall integrated circuit embedded in the microchip 20.
A traditional method used throughout the industry for positioning probes 12 in the required position on metal (or ceramic) probe ring 13 uses a film template, which generally consists of Mylar.TM., to fix the position of probes 12 in relation to the desired position on probe ring 13. Holes are typically drilled or punched in the template in a pattern that generally coincides with the location of the target area of contact pads of the microchip 20 to be tested. The bent tip of a probe 12 is then inserted into each hole after which probe ring 13 is bonded to the arrayed probes by means of an epoxy cement, which forms a single probe ring assembly 50. Probe ring assembly 50 is affixed to central opening 11 of printed circuit board 10 with cement and each probe 12 is soldered to a specified contact on the printed circuit board 10. Probe tips of probes 12 are then sanded to achieve a uniform length. Each probe 12 is then aligned (also known as "X-Y" positioning), so that it generally contacts the target area of the specified microchip 20 contact pad. Each of these steps are typically performed by hand.
Since all of the contact pads must be simultaneously engaged in order to carry out testing operations, it is essential that all of the probe tips of probes 12, electrically contact its target contact area(s) at the same time. In addition, since all of the contact pads generally lie in a common geometric plane, it is essential that the probe tips of probes 12 lie in a plane parallel to the common microchip plane of microchip 20. Consequently, a fundamental requirement of probe card assembly 50 is planarization (also known as "Z" or height positioning) of the probe tips. The nature of conventional probe card assemblies 50 and the character of the assembly fixtures for setting up the positions of probes 12 for such probe cards assemblies 50 are such that it is virtually impossible to assemble probes 12 with probes 12 lying exactly in the same plane. There are simply too many variables to control in existing manufacturing processes, especially in manufacturing processes that consist of numerous of steps that are performed by hand. These variables reduce the quality of the product as well as inhibit the development of an automated approach. In short, in light of the small tolerances involved with manufacturing probe rings 13 and probe card assemblies 50, slight errors and variances produced by steps performed by hand become major problems.
In addition to the well recognized need for accurately positioning each probe card assembly 50 on specified X, Y and Z axes with respect to the target contact pads on the microchip 20, there is an additional need for exact alignment of probe card assembly 50 on a specific rotational or theta (.theta.) axis. In particular, probe card assembly 50 is designed and built not only to test specified circuits and subcircuits on a microchip; it is also designed to be installed on and be used with automated test equipment. The construction of certain automated test equipment is generally such that probe card assembly 50 is fit to a component of the automated test equipment designed to allow for small rotational theta (.theta.) adjustments in the positioning of probe card assembly 50. Ideally, each probe card assembly 50 built for a given type automated test equipment would fit to that particular piece of automated test equipment in such a manner that the probe tips of each probe 12 of each probe card assembly 50 of a given design would engage the target areas of the contact pads of microchip 20 in precisely the same location, thereby requiring no adjustment when installing a new card 50. When this is not the case, the automated test equipment operator must manually adjust the orientation of the probe card assembly 50 by something on the order of two to fifteen degrees on the theta (.theta.) axis each time a new probe card is installed. This results in lost production each time a probe card assembly 50 is changed and adjusted. In addition, existing manufacturing methods are unable to reliably and uniformly replicate the X-Y positioning of each probe card component in relation to every other component, or in relation to the target pads on the microchip, for a card of a given design. Positioning of component to component in the manufacturing process is largely a subjective matter varying from technican to technician and from time to time. As a result, while more modern probers may, in some situations, perform the wafer to probe card alignment automatically (and fairly rapidly), there is still a time penalty associated with the use of traditional probe cards, such as probe card assembly 50, because of an inability of the industry to replicate the manufacture probe cards assemblies 50 having low rotational (or theta axis) and/or x-y, tolerance.